How to tell? Turbo or NA Master Cylinder

[benzyne]

I'm the 4th owner of a '78 SC. The second owners did a lot of work (like steel turbo flares, torsion bars and sway bars). I'm discovering little upgrades everytime I look underneath the car.

I've recently bought a 993 kit to upgrade the brakes. The kit requires a 930 master cylinder. My question is, is there any way that I can check which master cylinder that I currently have in my SC without taking the old one out (with a quick inspection, I can see G 36 cast into the MC)? The brakes on my car have a firmer feel that other SC's that I've driven. I'm wondering if the PO had already swapped out MC but not the calipers/rotors. If I can find out for certain beforehand, I won't be in the situation of buying a new MC and finding that I didn't need it.

Thanks in advance.

[spuggy]

I would think that SC brakes with a 930 M/C would be far too insensitive - a small pedal movement would move too much fluid and they'd tend to lock too easily. It would be difficult to modulate the brakes correctly.

An under M/C'd car will have too much pedal travel and the pedal may feel soft. Because it doesn't move enough fluid.

You could check the part # or measure the bore diameter to be sure what you have.

[tonythetarga]

The normal master cylinder is a 19mm and the turbo is 23mm. The link below is to the Pelican Parts section on m/c's. There are different part numbers; a 911 and 930 series. Check and see if you can find other numbers on the piece.

http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_BRKhyd_pg3.htm#item10

I imagine the exterior housing can be measured and compared between "known" m/c's of both sizes.

edit: I just checked my old 19mm and see no part number on the exterior. I measured the exterior of the housing from the side (as it sits in the car) and got 1 3/16" diameter. It is difficult to measure in the car with the ductwork and fan housing there.

[Bill Verburg]

Originally Posted by tonythetarga

The normal master cylinder is a 19mm and the turbo is 23mm. The link below is to the Pelican Parts section on m/c's. There are different part numbers; a 911 and 930 series. Check and see if you can find other numbers on the piece.


I imagine the exterior housing can be measured and compared between "known" m/c's of both sizes.

edit: I just checked my old 19mm and see no part number on the exterior. I measured the exterior of the housing from the side (as it sits in the car) and got 1 3/16" diameter. It is difficult to measure in the car with the ductwork and fan housing there.

All n/a SCs come w/ a vac. boosted 20.6mm m/c
like this one


the 930s from MY78 to 89 come w/ vac boosted 23.8mm like this one



the easist way to tell if you can't make out the size that used to be embossed on the side is to look at the business ends
23.8 on left 20.6 on right

[benzyne]

Thanks everyone for your help. Happy holidays.